Minggu, 11 Oktober 2009

Carbohydrates

What are carbohydrates? Carbohydrates are the main source of energy for the body. Those carbohydrates come from the plant-based foods that you eat. You can either use carbohydrates right away for your energy needs or your body can convert them into fat to use later. There are three types of carbohydrates -- sugars, starches and fiber.

First, a Little Chemistry

No matter how big they are, all carbohydrates are made of carbon, hydrogen and oxygen with the general formula of Cm(H2O)n. For example, a simple little sugar molecule like glucose is made up of six carbon atoms, 12 hydrogen atoms and 6 oxygen atoms. It is shaped like a hexagon and has the formula C6(H2O)6. A large starch molecule can be made of many little sugar molecules attached together, which forms a long chain. The little m and n in our general formula, Cm(H2O)n, can run into the hundreds.

Simple Sugars

Simple sugars are little molecules made up of one or two sugar units. In nutrition, the most basic simple sugar is glucose, C6(H2O)6, and it is the type of sugar our bodies and brains use for energy every day. Glucose is called a monosaccharide, which means "single sugar." Other monosaccharides include fructose, galactose, and ribose. Fructose is found in fruits and in vegetables, galactose is found in milk and ribose is best known as a component in ribonucleic acid, which is a part of genetic transcription and is found in the cells in our bodies.

I don't want to get much deeper into the chemistry of simple sugars, but it is important to know that the single sugars glucose, fructose and galactose can form different combinations to become disaccharides, a term that means "two sugars.” These sugars include:

Lactose (milk sugar) is made up of glucose and galactose molecules. People who are "lactose intolerant" can't digest this sugar properly.

Sucrose (table sugar) is comprised of glucose and fructose molecules. This is the white powdery or granular substance we typically refer to as "sugar" when we are cooking or baking.

Maltose (malt sugar) is produced during the malting of cereals such as barley.

Simple sugars are water-soluble and sucrose, or table sugar, is easy to digest. The individual glucose and fructose molecules are quickly absorbed into the bloodstream via the small intestine. This can be a problem for people with diabetes or metabolic syndrome who have to watch their blood sugar, or blood glucose levels.

Complex Carbohydrates

Complex carbohydrates are long chains of the single sugar units. For example, the complex carbohydrate we know as starch is made up of many glucose units. These complex carbohydrates can be in the shape of long chains, or the chains can form branches. The complex carbohydrates include:

Starch, the energy storage form of carbohydrates found in plants, especially in the seeds and roots. Starch is made up of many glucose units linked together. Starchy food examples include rice, wheat, corn, carrots and potatoes. Starches are not water-soluble and require digestive enzymes called amylases to break them apart.

Glycogen, the energy storage form of glucose found in the muscles and livers of animals. You don't consume any carbohydrates when you eat meats; however, the amount of glycogen in animal tissue at the time of slaughter does affect the pH of meat.

Cellulose, the structural component of plants. Cellulose helps plants keep their shape; so in a way, cellulose acts like a plant skeleton. We are unable to digest cellulose; however cellulose is one of the important components of fiber, along with lignin, chitin, pectin, beta-glucan, inulin and oligosaccharides.

Dietary starch and cellulose are the complex carbohydrates that are important in nutrition. Potatoes, dry beans, grains, rice, corn, squash and peas contain a large amounts of starch. Vegetables like broccoli, cauliflower, asparagus, lettuces and other greens are not starchy. That is because the stems and leafy parts of plants do not contain much starch, but they do contain more cellulose. Since we can't digest cellulose, that means that the green and leafy vegetables contain fewer calories than the starchy vegetables.

Carbohydrates and Metabolism

The body begins the process of breaking carbohydrates down into their individual monosaccharides almost before we start to eat them. When you smell the delicious aroma of fresh-baked bread or think about that tasty chocolate that you're about to consume, your mouth begins to water. Since table sugar is water-soluble, it begins to dissolve in the saliva in your mouth. Your saliva also contains a small amount of amylase, which is an enzyme that starts to break starch down into glucose while you are chewing.

Carbohydrate digestion is continued in the small intestine where pancreatic amylase is secreted, which breaks down the rest of the carbohydrates. The individual monosaccharides are then absorbed into the blood stream. Once in the blood, the monosaccharides are either used for energy, stored in the liver and muscles as glycogen, or if there is more energy available than you can use, they are converted and stored as fat.

The storage of glucose is triggered by insulin, which forces your body to store any extra blood sugar as glycogen. People with diabetes or metabolic syndrome either can't produce enough insulin or they are not sensitive enough to the insulin they produce and need to regulate their blood sugar with medications, insulin or dietary changes.

Your body prefers to use glucose as the main source of fuel for daily activity. Your muscles need glucose to move and your organs need glucose to function, including your brain. While the body can make glucose from extra dietary protein and fats you may eat, it is suggested that half of your daily calories come from carbohydrates. Try to get your carbohydrates from healthy sources such as whole grains, fruits and vegetables. Cookies, sodas, candy and other sweets are not so healthy.

An average healthy diet should have half of your daily calories coming from carbohydrates. One gram of carbohydrate, whether is it is sugar or starch, contains four calories. One slice of bread has about 12 grams of carbohydrates. One typical chocolate bar may have about 50 grams of carbohydrates. A medium potato has about 35 grams of carbohydrates.

Although all carbohydrates have four calories per gram, some sources of carbohydrates are better for your diet than others. Fruits, vegetables, legumes, nuts, seeds and grains are healthier than candy, sodas and pastries. Why? The healthy carbohydrate sources have great amounts of vitamins, minerals, phytochemicals and fiber, all of which are vital to good health. Candy, sodas, pastries and other junk foods usually are poor sources of nutrients and sometimes we refer to these foods as having "empty calories." This means the foods have lots of calories with little or no nutrition.

Since you need half of your calories from carbohydrates, you can calculate how many you need per day. For example, let's say a person needs 2,000 calories per day. That means that 1,000 calories should come from carbohydrates (2,000 X 0.5). Since each gram of carbohydrate has four calories, then you divide 1,000 by four (1,000/4) to get 250. A person who needs 2,000 calories each day needs about 250 grams of carbohydrates per day. Of those 250 grams, about 10 percent can come from added table sugar and sweeteners. That would be about 25 grams for a 2,000 calorie per day diet. That would equal about half of a candy bar, or less than one can of sugary soda. Unfortunately many people exceed that amount every day.

In order to meet your carbohydrate requirement each day, you need to know how many carbohydrates are in all of the foods you eat. It really is impossible to list every carbohydrate containing food here, however, here are some approximate amounts from common examples:

One slice of bread - 12.5 grams total, of which 10 grams are starch and less than one gram is fiber

One cup of pasta - 43 grams total, of which 36 grams are starch and 2.5 grams are fiber

One medium apple - 19 grams total, of which eight grams are starch and three grams are fiber

One Snickers candy bar - 63.5 total grams, of which 53 grams are sugar, two grams are fiber

One cup of raisin bran cereal - 43 grams total, of which seven grams are fiber, 17 grams are starch and 16 grams are sugar

One cup of sugar frosted corn flake cereal - 28 grams total, of which 15 grams are starch, one gram is fiber, 12 grams are sugar

One four ounce glass of red wine - three grams total, of which, less than one gram is sugar

You can search for more carbohydrate information online for all of your favorite foods at Calorie Count Plus.

Nutrition Facts labels on packaged foods will also list the amount of carbohydrates per serving. It takes a little extra time and effort to look up the carbohydrate counts for all of the foods you eat, but with experience you will begin to have a good idea of approximate calorie counts and carbohydrate counts.

This Week's Assignment

Well, you made it through lesson one and I have an easy assignment for you. You have learned about carbohydrates and why your body needs them. I want you to focus on eating healthful carbohydrates by increasing the amount of fruits and vegetables you eat. This week I want you to choose three new fruits or vegetables that you have never eaten before. You may eat them as snacks or as part of your regular meals. You may wish to continue to try new foods once each week or once a month after that.